A modified version of the Simpson index is used to assess similarities between the Early Triassic tetrapod faunas of Australia, Antarctica, India and South Africa. This index takes into account the relative abundances of taxa, and not merely their presence or absence. Antarctic, Indian and African faunas are all found to be very similar — one to another and each to a hypothetical ‘average’ fauna. The Australian fauna is distinctly different: it resembles other faunas in terms of the presence or absence of taxa, but it differs greatly in the relative abundances of those taxa. Most significant of those differences is the abundance of labyrinthodont amphibians and the commensurate rarity of reptiles. The unusual composition of the Australian fauna might be explained to a large extent by geographic isolation.